It is known that upon color development of silver halide color photographic materials, the oxidation products of aromatic primary amine color developing agents react with couplers to form indophenol, indoaniline, indamine, azomethine, phenoxazine, phenazine and similar dyes, thereby forming color images. In this system, color reproduction is usually accomplished by the subtractive color process; silver halide emulsions selectively sensitive sensitive to blue, green and red, and yellow, magenta and cyan color image-forming agents in a complementary relation therewith are used. For example, acylacetanilide or dibenzoylmethane type couplers are used to form yellow color images; pyrazolone, pyrazolobenzimidazole, cyanoacetophenone or indazolone type couplers are mainly used to form magenta color images; and phenol type couplers, such as phenols and naphthols, are mainly used to form cyan color images.
It is also known that couplers are used not only to form dye images as described above but also for the purpose of releasing photographically useful groups. For example, U.S. Pat. Nos. 3,227,554 and 3,148,062, and Journal of the American Chemical Society, Vol. 72, page 1533 (1950) disclose couplers which release a development inhibitor or a dye from the coupling position thereof on reacting with the oxidation products of color developing agents.
Further, U.S. Pat. No. 3,705,801 discloses couplers which are capable of releasing a bleach inhibitor from the coupling position thereof after the reaction of the couplers with the oxidation products of the developing agents. More recently, Japanese Patent Application (OPI) No. 150845/82 discloses couplers which release a fogging agent from the coupling position thereof after the reaction of the couplers with the oxidation products of the developing agents.
Moreover, compounds which do not form dyes but release a photographically useful group upon the reaction with the oxidation products of the developing agents have also been known. For example, U.S. Pat. No. 3,930,863 discloses hydroquinones which release a development inhibitor.
As is well known from the above-described patent specifications, compounds releasing a photographically useful group are used for purposes such as improvement in color reproducibility, improvement in graininess, improvement in sharpness, or increase of sensitivity.
It is common knowledge in the photographic art that a technique to control the rate of releasing a photographically useful group and the rate of diffusion into an emulsion is more important than a technique to control the photographic function of the photographically useful group in the compounds capable of releasing a photographically useful group. It is also disclosed that as the diffusibility of the development inhibitors released increases, the sharpness is improved as described in U.S. Pat. No. 4,500,634. As an example of such techniques, couplers which release a photographically useful group having a timing group are proposed in U.S. Pat. Nos. 4,248,962 and 4,409,323, etc. These known couplers have good properties to some extent since the increase in the rate of coupling with these couplers is recognized in comparison with couplers wherein the photographically useful group is directly connected to the coupling position (for example, couplers as described in U.S. Pat. No. 3,227,554, etc.).
However, with these compounds the degree of diffusion of photographically useful groups into an emulsion is low and further improvement of the photographic properties has been desired. Furthermore, known couplers having a timing group have a problem in stability thereof during preservation of films containing them after coating, and they are disadvantageous in that their function is decreased or desensitization or formation of fog is accompanied by decomposition thereof.